Where condition inside json_agg in postgres - postgresql

Question

I'm trying to return a JSON object from postgres that looks something like this:
[
{id: 1, name: "some organisation name", alias: [{alias:"alt name"}, {alias:"another name"}]}
...]
My query below works fine, except that I want to add a where condition, referencing the org_aliases table
SELECT json_build_object('id', table1.id, 'name', table1.name, 'alias', a.alias) as json
FROM orgs table1
CROSS JOIN LATERAL (
SELECT json_agg(agg) AS alias
FROM (
SELECT table2.alias as name
FROM org_aliases table2
WHERE
table2.org_id = table1.id
) agg
) a
WHERE
table1.name ilike 'nspcc'
or table2.alias ilike 'nspcc';
It fails on the last line (missing from condition on table2). I can see why it doesn't allow me to do this, as I'm referencing something inside a sub query.
My question, is what's the best way to handle this?
My only idea is that I need to join the org_aliases again so I can add a where condition. But if anyone has a better idea for how I structure the query to avoid duplication, that would be amazing.

Answer 1

Not sure if it's exactly what you're looking for, but it does give you the required result for your example:
SELECT
json_build_object('id', orgs.id
, 'name', name
, 'alias', json_agg(
json_build_object('name', alias)
)
)
FROM orgs
LEFT JOIN org_aliases ON orgs.id = org_aliases.org_id
WHERE name ILIKE '%dave%'
OR alias ILIKE '%dave%'
GROUP BY
orgs.id, orgs.name;
Edit: I would use a CTE to first find my target id and then get alle the data that I need. This makes it easy to understand (and debug):
WITH target AS (
SELECT orgs.id
FROM orgs
LEFT JOIN org_aliases ON orgs.id = org_aliases.id
WHERE name ILIKE '%dave%'
OR alias ILIKE '%dave%'
)
SELECT
json_build_object('id', orgs.id
, 'name', name
, 'alias', json_agg(
json_build_object('name', alias)
)
)
FROM target
JOIN orgs ON target.id = orgs.id
LEFT JOIN org_aliases ON orgs.id = org_aliases.org_id
GROUP BY
orgs.id, orgs.name;